This invention relates to a novel combustible, non-metallic cartridge case, and particularly to a porous, fiber reinforced nitrocellulose cartridge case provided with a composite coating, which is resistant to water and oil.
Combustible cartridge cases are generally composed of nitrocellulose, reinforcing fibers, and a resinous binder. A case of such type is filled with a propellant and fitted with a primer and a projectile to form a cartridge. Compared with metallic cases, the non-metallic cartridge cases possess the dual advantages of lower weight and cost.
A common method of fabricating combustible, non-metallic cartridge cases comprises dispersing nitrocellulose fibers or powder, reinforcing fibers, such as kraft and other cellulosic fibers, and/or synthetic fibers, such as acrylics and polyesters, together with resin binders and other components, i.e., stabilizers, etc., in water and collecting the fibers on a felting die. The felted fiber form is then molded into the desired shape using appropriately shaped matched molds, cured and dried. The finished cartridge case has a porous fibrous structure, which must be maintained to ensure the rapid propagation of the flame through the case material during firing. However, due to its porous structure and content of fibers, particularly cellulosic fibers, the non-metallic cartridge case will absorb liquid water as well as permit the penetration of water vapor, which adversely affects the firing and ballistic performance of the ammunition and causes incomplete combustion of the cartridge case. In addition, contact with oily substances, such as hydraulic fluids, also degrades the combustion characteristics of such non-metallic cartridge cases.
Various attempts to overcome the aforesaid deficiencies have included coating the cartridge case surface with a plastic film, such as nitrocellulose, alkyd resins, polyethylene resins and polyvinylbutyral resins. Generally, it was found that if a coating was thick enough to protect the cartridge case against both liquid water and water vapor, the flame could not propagate throughout the case during the firing cycle with the result that the case did not burn completely and left residue in the gun. On the other hand when the amount of coating was reduced so that the coating did not interfere with the combustion of the case, the coating failed to adequately protect the case against the penetration of liquid water and water vapor, which also produced an incomplete combustion of the case with resultant residue in the gun. Such residue presents an intolerable hazard, since it can smolder and cause accidental preignition of the cartridge case of the next round loaded into the gun. In addition, absorbed water or water vapor degrades the ballistic performance of the ammunition.
An object of the present invention is to provide a coating, which will render the combustible cartridge case insensitive to water in both liquid and vapor form and oil.
Another object of the invention is to provide a combustible cartridge case whose exterior surface is provided with a coating, which renders the case substantially impermeable to water and oil, so that upon firing of the ammunition, little, if any, residue will remain in the gun due to the coating or the absorption of water or oil by said case.
The foregoing and other objects will become apparent from the following disclosure.